INTRODUCTION: Atlanto-axial instability due to Rheumatoid arthritis has been treated by posterior C1/C2 wiring techniques supplemented with bone graft. Magerls technique of Transarticular fixation provides a three-point fixation by eliminating motion, promoting fusion, increased mechanical strength and treating instability. It allows fixation across the plane of movement and prevents basilar invagination.

The clinical results of transarticular fixation are satisfactory in terms of clinical outcome with few complications. However there are concerns that these patients develop subaxial kyphosis. It is important to highlight that none of these patients in our series had supplementary wiring techniques with TAS The purpose of this study is to analyse postoperative Xrays of patients who have undergone transarticular atlantoaxial fixation and look at the following parameters;

What percentage of patients develop subaxial kyphosis?

Are the ADI and PADI maintained postoperatively?

Is there a late failure rate of TAS despite the absence of supplementary wiring techniques?

MATERIALS & METHODS: 15 patients underwent pre and postoperative cervical spine X-rays in the AP and lateral projections. In addition flexion/extension views were also obtained pre and postoperatively.

We analysed the following parmeters:

Pre and Postoperative ADI and PADI.

C0/C1, C1/C2, C1/C7, C2/C7 angles

C2/C3 slip and C2/C3 osteoarthritis

Any breakage or pullout of screws.

Postoperative basilar invagination.

It is important to highlight that all these 15 patients had bony fusion at the C1/C2 joints and these findings have been analysed and published in the clinical counterpart of this study (Fusion rates 97% in 36/37 patients).

RESULTS: As highlighted, the clinical outcome of these patients has been published. We would like to present the radiological parameters of this subgroup of patients. The ADI improved in 13 patients with a preoperative median of 7 and postoperatively 3.5. The preoperative and postoperative PADI remained at 15. The C0/C1 angle changed from 12 to 17 postoperatively. The C2/C7 angle changed from 21 to 26 postoperatively. C1/C7 angle changed from 39 to 41. The spinal cord diameter remained at 15 pre and postoperatively.

There was only 1 patient with C2/C3 slip on flexion/extension views. 2 patients developed subaxial kyphosis with evidence of significant disc degeneration on preoperative imaging.

There are some interesting conclusions from these 15 xrays.

Only 2 out of 13 patients have developed a subaxial kyphosis.

The 2 patients that have developed subaxial kyphois had subaxial disc degeneration at the level of the kyphois

There was only 1 patient with a C2/C3 spondylolisthesis on flexion/extension.

The ADI and SAC were maintained at the craniocervical junction.

There is no late failure rate despite the absence of a modified gallie fusion